May Cause

Juxta-articular soft-tissue mass

May Be Caused by

 Common

Gout

Infectious arthritis

Juvenile rheumatoid arthritis

Lyme disease

Psoriatic arthritis

Reiter syndrome

Rheumatoid arthritis

Synovitis

Trauma with hemorrhage

 Uncommon

Acute rheumatic fever

Allergic reaction

Avascular necrosis

Bleeding tendency

Calcium pyrophosphate dihydrate crystal deposition disease

Drug reaction

Hemangioma

Hemophilia

Insect bite

Juvenile chronic arthritis

Leukemia

Lymphoma

Metastatic bone neoplasm

Neuropathic arthropathy

Pigmented villonodular synovitis

Primary bone neoplasm

Sickle cell disease

Synovial neoplasm

Synovial osteochondromatosis